In digital imaging systems, color generally is represented by coordinates in a multi-dimensional “color space” having three or more channels. Common examples include the well-known RGB and YUV color spaces. In the RGB color space, pixels are specified using coordinates (also referred to as pixel sample values or sample values) that represent intensities of red, green and blue light, respectively. In the YUV color space, pixels are specified using coordinates (pixel sample values or sample values) that represent a luminance value and two chrominance values.
Currently, many image capture, processing, and display devices can only handle pixel sample values having a small dynamic range of 256 (28) discrete values per channel, represented by 8 bits. Such images can be described as having a “bit depth” of 8 bits. In a typical RGB digital image having 8 bits per channel (8 bpc) in red, green and blue color channels, only 256 different values are possible for each of the red, green and blue pixel sample values. Other values (e.g., alpha or opacity values, luminance values, and other such values) also may be constrained by low dynamic range limitations. Some devices can handle up to a 10- or 12-bit dynamic range per channel. However, the human vision system can detect a wide luminance range of 14 orders of magnitude, which translates to around 46 bits. Luminance values in nature can be as high as 108 candela/m2 in bright sunlight, and as low as 10−6 candela/m2 on the underside of a rock on a moonless night.
High dynamic range (“HDR”) imaging presents a more versatile and natural image representation in line with the human vision system. HDR images can present a dynamic range higher than the traditional 8-bit, 10-bit and 12-bit representations to achieve a far higher image quality. HDR images can be used in the same kinds of devices and software tools that process conventional images if the HDR image format is compatible with the device or tool. Several HDR image formats have been developed, and cameras, computer graphics, and display devices have begun to produce, process and display images with increasing dynamic ranges.